In applying electronic instruments to temperature compensation and temperature detection, thermistor elements have hitherto been widely used. In the case where a thermistor element is used for temperature detection, properties which the sintered body constituting the thermistor element is required to have are (1) a small B-value; (2) the change of resistance during the thermal history of the element is small; and (3) the dispersion of resistance value and of B-value are small. The B-value as referred to herein is an index to express a change of resistance in a prescribed temperature range, and the smaller the value, the smaller the change of resistance with change in temperature. Then, a thermistor element formed of this sintered body having the foregoing properties has (1) a wide temperature detection range, (2) excellent heat resistance, and (3) excellent precision of temperature detection.
As the sintered body for a thermistor element, there is disclosed a sintered body containing (Y, Sr) (Cr, Fe, Ti)O3 as the major component and exhibiting stable resistance in the temperature region of from 300 to 1,000° C. (for example, Japanese Patent No. 3,254,595). The temperature dependent resistance characteristics of the sintered body for thermistor element as disclosed in this Japanese Patent No. 3,254,595 are that the resistance value is about 100 kΩ at 300° C. and about 80 Ω at 900° C., and that the B-value at from 300 to 1,000° C. is about 8,000 K. However, since the sintered body contains Ti as the constituent element, the B-value tends to become large, and the resistance value at temperatures not higher than 200° C. is large, on the order of MΩ, so that it is indistinguishable from insulation resistance, and temperature detection cannot be achieved.
Incidentally, by changing the proportion of elements constituting the foregoing composition, for example, it is possible to adjust the resistance value at 100° C. to be not more than 500 kΩ, the value at which it is distinguishable from insulation resistance, so that temperature in the vicinity of 100° C. can be detected. However, since the Cr element as the constituent element is readily volatile, there was encountered a problem that the B-value varies among individual elements (thermistor sintered bodies) according to the amount of volatilization.
Also, there are disclosed sintered bodies for thermistor elements containing [Y(Cr, Mn)O3+Y2O3] as the major components (see, for example, JP-A-11-251108 and JP-A-2002-124403). Since these sintered bodies contain Cr, a dispersion of the B-value among the individual sintered bodies is inevitable.
In the light of the above, there is demand for a sintered body for thermistor element having excellent temperature detecting performance in the temperature range of, approximately 100 to 1,000° C., preferably lower than 300° C., and having a small dispersion of a B-value among individual elements.